Electron discharge device



P 3, 1940- s. F. BRETT 2,213,543

ELECTRON DISCHARGE DEVICE Filed July 13, 1938 INVENTOR. GEORGE FA/RBURA/ BRETT BYa W v A TTORNEY.

Patented Sept. 3, 1940 UNIT D ESTATES.

ELECTRON DISCHARGE nEvIcE George Fail-burn Brett, London, England, assignor to Radio Corporation of America, a corporation of Delaware I Application July 13, 1938, Serial No. 218,911 England August '7, 1937 Q1 3 Claims. (01. 250-475).-

,This invention relates to electron discharge tubes and has for its objectto providean improved form of tube suitable'for use for generating ultra-high frequency oscillationswith relativelylarge outputs. v v V I Although the invention isnot limited to its application'to theprovision of tubes for oscillation 'generation at any particular frequency it is well suited for the provision of ultra-high frequency oscillationsin the region of 20 to 100 cms. in wavelength, and, as will be seen later, provides tubes which'willproduce such oscillations by virtue of inherent negative resistance characteristics without relying upon secondary emission efiects.

As is well known great practical difliculties are experienced in satisfactorily producing high power'ultra-high frequency oscillations at frequencies of the orderabove mentioned. When ordinary triodes are sought to be used for this purpose inherent and serious difficulties arise due to the finite electron transit times in the valve and due to space charge eifects. Although various magnetron tube arrangements, arrangements of the Barkhausen Kurz and Gill 'Morell type and other arrangements which will operate at very high' frequencies are: known, the known arrangements are usually comparatively unstable, inefficient, c'omplexfand almost always are difficult to modulate. e e

The present invention seeks to provide improved tubes which will produce high frequency oscillations by inherent negative resistance effects without depending on secondary emission effects, and which in contrast with known magnetron arrangements, lend themselves to satisfactory and eficient modulation.

According to this-invention an electron discharge tube oscillator comprises a tub'e havin'g an electron gun system including at least a cathode, an apertured control electrode and. an apertured accelerator anode said'last two elec trodes having apertures aligned with the cathode, and an additional anode electrode external to the gun and having a surface out of the direct line from the cathode through the two aligned apertures; and means for applying a magnetic field in a direction approximately at right angles to the said direct line whereby electrons passing from the cathode throughthetwo said aligned apertures-do not proceed in said direct line but in a path which is bent round towards the aforementioned surface of the external anode.

The novel features which-I believe to be characteristic of my invention are set forthwith particularity in-the appended claims, but the invention itself will best be understood by refer ence to the following description taken in connection with the-accompanying drawing in which Figure 1 is a transverse section ofan electron discharge device made according to my invention and Figure 2 is a graph showing certain characteristics of a tube made according to my invention Referring to Figure 1, which is a schematic cross section of one form of tube for use in carrying out this invention there is employed a straight cathode which may be and preferably is of the indirectly heated equi-potential type said cathode being concentrically positioned within a cylindrical control electrode G which is in turn concentrically positioned within an accelerator anode A also of cylindrical shape. control electrode G is close to the cathode'and the'accelerator anode A is close to the control electrode. Each of these electrodes G and A consists of a substantially cylindrical plate which may be either closed'or open at its ends having a slot or gap running parallel to the cathode, the two slots or gaps (one in the control electrode and the other in the accelerator anode) being substantially of the same length as the cathode and co-planar therewith. The electrodes just mentioned constitute an electron gun which is: concentrically surrounded by an eX- ternal cylindrical anode AA whose radial distance from the cathode is considerably greater than that of the accelerator anode A. The external anode may be either open or closed at its ends as may be desired' A magnetic field The generated in any convenient way by means for example of electromagnet coil M, is applied to thread the electrode system above described Withits lines of force running parallel or subsome positive potential-of, say, 50 to 500 volts a flat ribbon sectioned beam of electrons will be produced. These voltages may be applied'from a source E. The characteristic connecting the voltage EA on the anode A with the current IA to this anode will be of the general form'shown in Figure 2. The intensity of the beam, for a given value of accelerator anode potential, will be dependent upon the potential of the control electrode G and will be capable of being modulated by modulating the control electrode potential. If the same positive potential is applied to the external anode as is applied to the accelerator anode, the beam emerging from the gun will be bent round into a circular path such Accordingly with a and external anodes, it is possible to cause. the electron beam to travel in a circular path back to the accelerator anode to strike thejsald anode along a line nearly opposite the aperture through which the beam is projected, said circular path just failing to touch the external anode. In this condition there will be zero current to. the external anode,since all the current will flow tothe accelerator anode. The value-I1 of this current will depend, among other things, upon the accelerator anode potential. With increase in accelerator anode potential assuming the external anode potential to remain fixed) the current produced by the electron gun will increase but at the same time the electron path will approachnearer and nearer to the external anode until finally for a potential V2 corresponding. to an accelerator anode current 12 the electron path touches the external anode AA. Any increase in accelerator anode potential beyond this point increases the current to the external anode but decreases that to the accelerator anode until, for some maximum value V3 of potential on the accelerator anode, the current thereto is practically zero all,the current now flowing to the external anode. Accordingly for a range of accelerator anode voltages between a'lower value V2 at which maximum current 12 flows to the accelerator anode and a higher value V3 at which substantially zero current flows to the accelerator anode, the accelerator anode characteristic will contain a negative resistance portion; that is to say, its slope will be downward. Thus a resonant circuit or device such as R consisting, of a condenser and inductance connected in the accelerator anode circuit may be excited to generate. and sustain oscillations. e

It may be noted that the electron path is circular only when the accelerator and external anodes are at the same potential but despite noncircularity of path at other potential relations, increase in accelerator anodepotential will cause the electrons to approach nearer the external anode. I

In order to obtain maximum steepness of the negatively. sloping part of the characteristic curve it is preferred so to adjust the various parameters that the electron path just fails-to touch the external anode when the twoanodes are at equal potential. The pathwill thenbe circular.- and therewill be obtained the advantage of the well known property that electrons emerging from the gun with a relativelywide angle of divergence will be brought to a focus on theother end of the path diameter of which the cathode is at one end. This, of course, involves that there will be a maximum change in acceleratoranode current for a given change-of accelerator anode voltage. Moreover, there will be maximum shift of focus for a given change in electron velocity.

' There are two main advantages of a system as described above 1) modulationis easily effected by the application of modulating potentials to the control electrode by means of a .modulating circuit M, and (2) althoughthe electron current alternates between the accelerator and external anodes, one "robbing the other, the electron beamdoes not have to traverse abrupt edges as is the case in those known oscillating electron beam generator systems wherein anelectron beam has to cross the boundary between two collector anodes at each half cycle. Since in the present system there are. no sharpelectrode edges which the electronbeam has to traverse, the dilficulties of burning due to high current changes at those edges are avoided and undesired secondary electron emission effects are minimized. Such electron emission as may occur will be dealt with by the applied magnetic field which will cause secondary electrons to return to the electrode of origin. If desired, either or both of the two anodes of the tube, may be carbonized and fitted with a cooling fin or fins to minimize secondary emission to assist to dissipate heatdue to electron bombardment and to assist in temperature equalization on the external anode, since owing to the fact that the electrons will bombard only a limited, localized area on this anode, there will be a tendency to form steep temperature gradients thereon. 7

While I have indicated the preferred embodiments of my invention of which I am now aware and have also indicated only one specific application for which my invention may be employed, it will be' apparent that my invention is by no means limited to the exact forms illustrated or the use indicated, but that many variations may be made in the particular structure used and the purpose for which it is employed without (ieparting from the scope of my invention as set forth in the appended claims.

What I claim as new is: i

1. An electron discharge tube having a straight thermionic cathode, a pair of solid concentric electrodes surrounding and coaxial with said cathode and including a control electrode and an accelerator anode, said control electrode and said accelerator anode. each having a single slotted aperture parallel to said cathode, said apertures being aligned and a cylindrical anode surrounding said cathode and said concentric electrodes and coaxial with said cathode, and means for inducing/a magnetic field parallel to said cathode and between said cathode and cylindrical anode.

2. An electron discharge tube having a straight thermionic cathode, a pair of solid concentric electrodes surrounding and coaxial with said cathode and including a control electrode and an accelerator anode, said control electrode and said accelerator anode having aligned slotted'apertures parallel to said cathode and a cylindrical anode surrounding said cathode and said concentric electrodes and coaxial with said cathode,

aperture parallel to said cathode, said apertures being aligned and a cylindrical anode surrounding said cathode and said concentric electrodes and coaxial with said cathode, the slots inthe control electrode and the accelerator anode being of substantiallythe same length as said cathode and parallel therewith, and means for inducing a magnetic, field parallel to said cathode and between said cathode and cylindrical anode.

GEORGE FAIRBURN, BRETTQ. 

